Method for pyrolysis and catalytic hydrogenation

ABSTRACT

A PRESSURE OF ABOUTF 200-2000 P.S.I.G. IS INTRODUCED INTO A LOWER PORTION OF THE REACTION ZONE DURING THE HEATING, AT AN UPWARD VELOCITY WHICH IS SUFFICIENT TO FLUIDIZE THE CATALYST. THE GAS WILL ALSO CARRY THE FINELY DIVIDED SPENT SHALE PARTICLES AND THE VAPORIZED, HYDROGENATED SHALE OIL UPWARDLY OUT OF THE REACTION ZONE.   A METHOD IS PROVIDED FOR PYROLYZING OIL SHALE WHILE SIMULATNEOUSLY HYDROGENATING SHALE OIL IN A SINGLE REACTION ZONE. BASICALLY, THE METHOD COMPRISES INTRODUCING OIL SHALE INTO THE REACTION ZONE, WHICH CONTAINS A FLUIDIZABLE HYDROGENATION CATALYST. THE OIL SHALE IS HEATED TO PYROLYSIS TEMPERATURES IN THE REACTION ZONE, WHICH VAPORIZES THE KEROGEN, PRODUCING A BREAKDOWN OF THE OIL SHALE, AND LEAVING FINELY DIVIDED PARTICLES OF SPENT SHALE. HYDROGEN UNDER

Feb, 23-, 1971 i HQEKSTRA 3,565,751

METHOD FOR PYROLYSIS AND CATALYTIC HYDROGENATION Filed May 28, 1969 if". y

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//V/ [/V7v, I Q Jam// 5 lzhziz United States Patent US. Cl. 208 12 Claims ABSTRACT OF THE DISCLOSURE A method is provided for pyrolyzing oil shale while simultaneously hydrogenating shale oil in a single reaction zone. Basically, the method comprises introducing oil shale into the reaction zone, which contains a fluidizable hydrogenation catalyst. The oil shale is heated to pyrolysis temperatures in the reaction zone, which vaporizes the kerogen, producing a breakdown of the oil shale, and leaving finely divided particles of spent shale. Hydrogen under a pressure of about 200-2000 p.s.i.g. is introduced into a lower portion of the reaction zone during the heating, at an upward velocity which is sufficient to fluidize the catalyst. The gas will also carry the finely divided spent shale particles and the vaporized, hydrogenated shale oil upwardly out of the reaction zone.

The present invention relates to an improved method for pyrolyzing oil shale while simultaneously hydrogenating the shale oil which is produced.

Shale oil is a valuable source of petroleum products, assuming that the oil may be removed from it with a high degree of efiiciency and at minimum expense. The source of petroleum products in oil shale is known as kerogen, a complex mixture of hydrocarbons and other organic compounds which act as a binder for the shale. When the oil shale is heated to pyrolysis temperatures, the kerogen is vaporized, producing shale oil which may be refined to make a wide range of petroleum products. A difficulty that has been experienced in the pyrolysis of oil shale lies in the fact that when the shale oil evolved is condensed, it tends to form high molecular weight compounds that cannot be further processed. This problem has been partially solved by pyrolyzing oil shale in the presence of hydrogen, which inhibits the formation of these high molecular weight products. However, the presence of hydrogen does not entirely prevent the formation of these undesirable products. Another difficulty with many of the processes that have been employed heretofore is that they lack efficiency in that they do not insure that all of the shale oil is removed from the shale.

Generally, the present invention relates to an improved method for pyrolyzing oil shale and simultaneously hydrogenating the shale oil in the presence of a hydrogenation catalyst, and in a single reaction zone. This simultaneous pyrolysis and hydrogenation insures maximum yield of high quality product. In carrying out the process, oil shale is introduced into a reaction zone which contains a conventional, fluidizable hydrogenation catalyst. The oil shale is heated in the reaction zone to pyrolysis temperatures, whereby to drive shale oil from the oil shale and to produce finely divided particles of spent shale as a result of the removal of the kerogen. Hydrogen is introduced into a lower portion of the reaction zone during the heating, under a pressure of about 200-2000 p.s.i.g. and at an upward velocity sufiicient to fiuidize the catalyst and to carry the finely divided spent shale particles and shale oil upwardly out of the reaction zone. Because of the presence of the hydrogen and a hydrogenation catalyst,

the shale oil is hydrogenated prior to removal from the reaction zone.

The invention will be best understood by reference to the following detailed description, taken together with the drawing, which is a diagramamtic illustration of a system adapted to carry out the method of the present invention.

As previously mentioned, the present invention permits the simultaneous pyrolysis of oil shale and hydrogenation of shale oil in a single reaction zone. This process is capable of being carried out either batchwise or continuously.

Before carrying out the process, a particulate, fluidizable hydrogenation catalyst is first delivered to the reaction zone. This hydrogenation catalyst should have a particle size range which is sufficiently small to permit the catalyst to be fluidized, yet sufiiciently large so that the catalyst will not be carried out of the reaction zone by the upwardly moving stream of hydrogen gas. Of course, the particular catalyst size required will depend upon the .density of the catalyst and upon the gas velocity involved.

As a general matter, in accordance with the present in vention, the hydrogenation catalyst should have a particle size in the range of about 0.01 to 0.5 inch.

Any conventional hydrogenation catalyst may be employed. Suitable catalysts include crystalline and amorphous silica-alumina, silica-zirconia-alumina, silica-mag nesia, alumina, etc., loaded with a suitable hydrogenation metal, such as platinum, palladium, molybdenum, cobalt, nickel, and the like, as is well known to those skilled in the art. The particular identity of the catalyst employed is not an important aspect of the present invention, although the catalyst should have a high degree of attrition resistance. For maximum efliciency, the catalyst particles are preferably spheroidal.

After the reaction zone has been charged with a hydrogenation catalyst, oil shale is introduced, and is heated to pyrolysis temperatures. The temperature should be controlled, however, so that it is not so high as to make hydrogenation impossible. That is, catalysts conventionally employed as hydrogenation catalysts will generally also serve as hydrocracking catalyst at higher temperatures, and under different reaction conditions. It is not usually desirable to have hydrocracking occur in the reaction zone. Of course, factors other than temperature, such as the velocity of the gas and the identity of the catalyst, are important in determining when hydrogenation will occur. As a general matter, however, the temperature should be controlled in a range of about 700-900 F. Below 700 F., pyroly- 818 does not occur at a sufliciently rapid rate, while above about 900 F. a sifinicant amount of hydrocracking may take place.

The heating of the oil shale in the reaction zone is accomplished by conventional means, such as by a furnace surrounding the reaction zone, electrical heating coils, etc.

Hydrogen is introduced into a lower portion of the reaction zone, preferably at the bottom of the reaction vessel, during the heating. The hydrogen gas should be under a pressure of about 200-2000 p.s.i.g., and should be delivered at an upward velocity sufiicient to fluidize the catalyst and to carry the finely divided spent shale particles produced in the reactor upwardly out of the reaction zone. In the preferred embodiment, the hydrogen gas is preheated prior to introduction into the reaction zone, providing a source for pyrolysis heat. The upward velocity of the gas which is required will again depend upon a number of factors, the most important of which is the catalyst particle size and density. However, those skilled in the the art will easily be able to select proper fluidization conditions once the catalyst has been selected. Sufficient fluidization occurs when the catalyst bed is eX- panded about 25 to or more beyond its volume when no gas is being delivered. Of course the upward flow of hydrogen must not be at a rate that is so high that any significant amount of catalyst is carried upwardly out of the reactor. For most catalysts, a gas feed rate in the range of about -20 feet per second is satisfactory.

Referring now to the drawing, the reaction zone in which the simultaneous pyrolysis and hydrogenation of the present invention are accomplished is defined by a reaction vessel 10. Before it can be introduced into the reaction vessel 10, raw oil shale must generally be delivered to a grinder or crusher 12 to reduce the shale particle size to a level Where it can be conveniently handled. The particle stize of the oil shale is not critical in the present invention, since, as previously mentioned, pyrolysis of the shale will cause a substantial reduction of the particle size after the kerogen has been removed. However, for ease of handling, the average particle size of the oil shale should be about one inch in diameter or less. After passing through the grinder or crusher 12, the raw oil shale is delivered through a transfer line 14 to a pair of storage hoppers 16. The transfer line 14- has two branches, each of which has a valve 18, so that the oil shale may be selectively delivered to either of the hoppers 16. Communicating with the bottom of the hoppers 16 are a pair of shale outlet lines 20, each having a valve 22. These shale outlet lines 20 converge to form a single shale delivery line 24. It can be seen that, by proper control of the valves 18, 22, one of the hoppers 16 may be maintained under elevated pressure, while the other is at atmospheric pressure, and is being filled with raw shale. That is, the upper valve 18 for one of the hoppers is closed, while the lower valve 22 is open, so that the hopper is pressurized, while shale is being delivered to the shale delivery line 24. On the other hopper, the lower valve 22 is closed, while the upper valve 18 is opened, so that this hopper may be filled with raw shale. This two-hopper system makes continuous delivery of shale possible without requiring depressurization of the system. Of course, if continuous operation were not desired, a single hopper could be employed. Similarly, a larger number of hoppers could also be employed, as those skilled in the art will understand.

After it emerges from one of the hoppers 16, the raw shale is conducted through the shale delivery line 24 to a dense phase solids heat exchanger 26, and then to a dilute phase solids heat exchanger 28, before introduction into the reactor 10. These heat exchangers 26, 28 permit the raw shale to be preheated prior to introduction into the reactor 10 by contacting it with hot, spent shale, as hereinafter described. After the raw shale has passed through the dilute phase heat exchanger 28, it is introduced into the reactor 10, preferably at a lower portion thereof.

Hydrogen from a make-up hydrogen source 30 is delivered to the reaction vessel 10 through a hydrogen input line 32. As shown in the drawing, the hydrogen input line 32 communicates with the reaction vessel 10 at the bottom, and delivers hydrogen upwardly through the vessel 10, where it is Withdrawn at a gas outlet line 34, communicatig with an upper portion of the reaction vessel 10. A compressor 36 provides the necessary hydrogen pressure and feed rate in the hydrogen input line 32. In the preferred embodiment, a hydrogen heater 38 is placed on the hydrogen input line 32 to preheat the hydrogen prior to introduction into the reaction vessel 10. As previously mentioned, the hydrogen is preferably delivered upwardly through the reaction vessel 10 at a feed rate of about 0.5-20 feet per second, and the system is maintained under about 200-2000 p.s.i.g. hydrogen pressure. In the most preferred embodiment, the hydrogen pressure is maintained in the range of about 400-600 p.s.i.g. At lower pressures, it is difficult to achieve efiicient hydrogenation, while at higher pressures it becomes difficult to maintain the catalyst in a fluidized state. The combination of preheating the catalyst, preheating the hydrogen, and delivering heat to the reaction vessel 10 (by conventional heating means, not shown in the drawing) heats the oil shale in the reaction vessel 10 to a temperature sufiicient to produce pyrolysis, yet insufficient to produce hydrocracking, and preferably in the range of about 700900 F.

The upwardly moving stream of hydrogen, which exits from the reaction vessel 10 through the gas outlet line 34, will carry with it vaporized, hydrogenated shale oil along with finely divided particles of spent shale. These finely divided shale particles will form a dilute phase in the gas, since no effort has been made to concentrate them at this point. In the preferred embodiment, the gas and shale particles are passed through the dilute phase solids heat exchanger 28, wherein heat is exchanged with the incoming raw shale as previously described. The gas and suspended solids are then delivered to one or more cyclone separators 40, wherein the solids are separated from the gaseous phase by centrifugal .force. The spent shale which is separated in the cyclone separators 40 from the gas phase is then delivered through a spent shale line 42 to the dense phase solids heat exchanger 26. Here, the solids are no longer in gaseous suspension, and may again be contacted with the incoming raw shale as previously described. After passing through the dense phase heat exchanger 26, the spent shale is delivered through the spent shale line 42 to a spent shale hopper 44. Hydrogen gas which is carried to the spent shale hopper may either be recycled or burned off, after removal from the hopper 44 through a hydrogen removal line 46. The spent shale in the hopper 44 is removed through a spent shale removal line 48.

The gas phase which is separated from the shale in the cyclone separators 4-0 contains hydrogen along with vaporized, hydrogenated shale oil. This combination of gases is delivered through a gas transfer line 50 to a high pressure fractionator 52. The gas transfer line 50 may optionally include a filter 51 to remove any remaining shale fines from the gas stream.

The fractionator 52, which is a conventional piece of equipment, separates the oil shale into the desired number of fractions. In the embodiment shown, the fractionator 52 has a naphtha fraction outlet line 54, a gas oil fraction outlet line 56, and a lower outlet line 58 for removal of the bottom fraction. The bottom fraction can be recycled to the reaction vessel 10 for further hydrogenation, can be used for fuel, or can be employed for other purposes, as is familiar to those skilled in the art.

The hydrogen which is separated from the fractionated shale oil in the fractionator 52 is removed via an upper outlet line 60. A portion of this hydrogen is delivered to a hydrogen recycle line 62, while the remaining portion is delivered to a motive hydrogen line 64. The hydrogen in the recycle line 62 is maintained at the proper pressure by a recycle compressor 66 before being returned to the hydrogen input line 32. This hydrogen is then recycled through the system as previously described. Losses of hydrogen which occur in the system are compensated by additional hydrogen from the makeup hydrogen source 30.

The pressure of the hydrogen in the motive hydrogen line 64 is increased by a motive hydrogen compressor 68. This hydrogen is then delivered to the raw shale storage hoppers 16, where it provides the necessary push to move shale through the system. Of course, conventional mechanical means such as auger conveyors and the like (not shown) may also be employed to assist in moving raw shale through the shale delivery line 24 to the reaction vessel 10. As shown in the drawing, the motive hydrogen line 64 is divided into two branches, one for each storage hopper 16. Each branch has a valve 70. Thus, motive hydrogen is only delivered to the particular storage hopper 16 which is being employed to deliver raw shale to the system, and for which the upper valve 18 is closed. It should be understood that this hydrogen, although referred to as motive hydrogen, does not necessarily produce a function of moving the shale in the system. This hydrogen may simply be present under sufiicient pressure to maintain the system filled with hydrogen, the actual movement of the shale being accomplished by suitable conventional mechanical means.

After a period of time, the hydrogenation catalyst in the reaction vessel 10 will become exhausted, and is removed through a catalyst outlet line 72 communicating with the bottom of the reaction vessel 10. Of course, it is also possible to continuously remove catalysts from a lower portion of the reaction vessel 10, regenerate it, and re-introduce the catalyst into an upper portion of the reaction vessel 10.

As those skilled in the art will understand, the foregoing description relates to a specific, preferred embodiment of the method of the present invention. Numerous modifications may be made without departing from the spirit and scope of the invention, which basically simply comprises a method for simultaneously pyrolyzing oil shale and hydrogenating the vaporized shale oil. It will also be appreciated that a particularly advantageous aspect of the present invention is that complete pyrolysis of the oil shale is virtually guaranteed. That is, the oil shale will not leave the reaction vessel 10 until it has been reduced to a particle size which is fine enough to be removed by the upwardly moving stream of hydrogen gas. The exhaustion of the oil shale is evidenced by this formation of fine particles, a particle size of about 0.003 inch being a typical average for disintegrated spent shale. This formation of fine particles occurs as a result of the removal and vaporization of the kerogen in the shale, and is enhanced by particle collisions within the reactor.

Obviously, many modifications and variations of the invention as hereinbefore set forth will occur to those skilled in the art, and it is intended to cover in the appended claims all such modifications and variations as fall within the true spirit and scope of the invention.

I claim:

1. A method for pyrolyzing oil shale and simultaneously hydrogenating shale oil in a single reaction zone comprising: introducing oil shale into a reaction zone containing fiuidizable hydrogenation catalyst; heating said oil shale to pyrolysis temperatures in said reaction zone, whereby to drive shale oil from said oil shale and to produce finely divided particles of spent shale; and introducing hydrogen gas into a lower portion of said reaction zone during said heating under a pressure of about ZOO-2000 p.s.i.g. and at an upward velocity suflicient to fluidize said catalyst and to carry said finely divided spent shale particles and said shale oil upwardly out of said reaction zone.

2. The method as defined in claim 1 wherein said catalyst particles have a diameter of about 0.01 to 0.5 inch.

3. The method as defined in claim 2 wherein said catalyst particles are spheroidal.

4. The method as defined in claim 1 wherein said hydrogen gas travels upwardly through said reaction zone at a rate of about 0.520 feet per second.

5. The method as defined in claim 1 wherein said oil shale is heated to about 700900 F. in said reaction zone.

6. The method as defined in claim 5 wherein said hydrogen is preheated prior to introduction into said reaction zone.

7. The method as defined in claim 1 further including the step of exchanging heat from said spent shale to said oil shale before introducing said oil shale into said reaction zone.

8. The method as defined in claim 1 further including the step of fractionating said shale oil.

9. A method for pyrolyzing oil shale and simultaneously hydrogenating shale oil in a single reaction zone comprising: introducing oil shale into a reaction zone containing a particulate, fluidizable hydrogenation catalyst having a particle size in the range of about 0.01 to 0.5 inch; heating said oil shale to about 700900' F. in said reaction zone, whereby to drive shale oil from said oil shale and to produce finely divided particles of spent shale; and introducing preheated hydrogen gas into a lower portion of said reaction zone during said heating under a pressure of about 200-2000 p.s.i.g. and at an upward velocity of about 0.5-20 feet per second to fluidize said catalyst and to carry said finely divided spent shale particles and said shale oil upwardly out of said reaction zone.

10. The method as defined in claim 9 further including the step of exchanging heat from said spent shale to said oil shale before introducing said oil shale into said reaction zone.

11. The method as defined in claim 9 further including the step of separating said spent shale from said hydrogen gas and recycling said hydrogen gas to said reaction zone.

12. The method as defined in claim 11 wherein said oil shale is continuously introduced into said reaction zone.

References Cited UNITED STATES PATENTS 2,639,982 5/1953 Kalbach. 2,707,163 4/1955 Thibaut. 3,346,481 10/ 1967 Johnsen.

CURTIS R. DAVIS, Primary Examiner US. Cl. X.R. 208l1 

